Pretensioners are used to rapidly pull in any slack in a safety restraint seat belt at the onset of a crash to securely restrain a vehicle occupant against forward movement and potential injury by collision with internal features of the vehicle. In addition, the pretensioning operation aims to pull the vehicle occupant into, or at least towards, the correct seating position to maximise the effect of a second restraint, such as an airbag.
A modern seat belt is known as a 3-point restraint because it is secured to the vehicle at three points arranged about the vehicle occupant to provide a diagonal torso section and a horizontal lap portion to hold the vehicle occupant in the seat. The belt is attached to the vehicle by a spring-loaded retractor tending to pull in the belt, and by a buckle for quick release of the belt.
Pretensioners can be at either the retractor or the buckle end of the seat belt. The present invention relates particularly to a retractor end pretensioner and aims to provide an improved and more compact pretensioner than hitherto known.